Permeation instruments are used to measure the transmission rate of a target analyte, such as oxygen, carbon dioxide or water vapor, through various samples, such as membranes, films, envelopes, bottles, packages, containers, etc. (hereinafter collectively referenced as “test films” for convenience). Typical test films are polymeric packaging films such as those constructed from low density polyethylene (LDPE), high density polyethylene (HDPE), oriented polypropylene (OPP), polyethylene terepthalate (PET), polyvinylidene chrloride (PVTDC), multi-layer polymeric films, etc. Typically, the film to be tested is positioned within a test chamber to sealing separate the chamber into first and second chambers. The first chamber (commonly referenced as the driving or analyte chamber) is filled with a gas containing a known concentration of the target analyte (commonly referenced as a driving gas). The second chamber (commonly referenced as the sensing chamber) is flushed with an inert gas (commonly referenced as a carrier gas) to remove any target analyte from the cell. A sensor for the target analyte is placed in fluid communication with the sensing chamber for detecting the presence of target analyte that has migrated into the sensing chamber from the driving chamber through the test film. Exemplary permeation instruments for measuring the transmission rate of oxygen (O2), carbon dioxide (CO2) and water vapor (H2O) through test films are commercially available from Mocon, Inc. of Minneapolis, Minn. under the designations OXTRAN, PERMATRAN-C and PERMATRAN-W, respectively.
Permeation instruments typically employ either a flow-through method or an accumulation method for sensing the presence of target analyte in the sensing chamber. Briefly, the flow-through method continuously flushes the sensing chamber with inert carrier gas to transport any target analyte that has migrated into the sensing chamber and deliver it to a remotely located target-analyte sensor. The accumulation method intermittently flushes the sensing chamber with inert carrier gas to transport any target analyte that has migrated into the sensing chamber and deliver it to a remotely located target-analyte sensor, thereby allowing target analyte to accumulate in the sensing chamber for accumulation periods between each sensing.
Permeation instruments typically employ a rigorous testing protocol that includes, in addition to periodic sensing of target-analyte concentrations found in the sensing chamber throughout a permeation testing period, periodic rezeroing throughout the permeation testing period and an individual zero upon conclusion of permeation testing period. Such additional measurements significantly increase testing period time but can be critical to ensuring accuracy of the resultant measurements, particularly when the test film is a superior target-analyte barrier and the concentration of target-analyte reaching the sensing chamber is low.
Accordingly, a substantial need exists for a permeation instrument capable of decreasing testing period time without compromising accuracy.